1. Field of the Invention
The present invention relates to a low impedance amplifier for use in detecting the structural abnormality of substances by detecting piezoelectricity and/or pyroelectricity generated in a structure composed of electrically conducting crystalline or non-crystalline substances with no band gap or a band gap of not higher than 0.008 eV.
2. Description of the Prior Art
The inventor invented "a method of detecting structural abnormality of substances" (disclosed in the Japanese Patent Laid-Open Patent Publication No. SHO62-259050). The basic circuit, shown in the FIGS. 6-1, 6-2, 7-1, 7-2, 8 and 9 attached to the above patent application, generates electrical phenomena such as piezoelectricity and/or pyroelectricity that would occur in a structure composed of electrically conducting crystalline or non-crystalline substances with no band gap. The method according to this invention comprises extracting the electrical phenomena through leads each connected to each of at least a pair of terminals provided directly on the simple and basic structure, and monitoring and measuring the thus extracted piezoelectricity and/or pyroelectricity, thereby accurately locating and identifying the extent of seriousness of the stress-caused structural abnormality of the structure.
As an invention related to the above disclosure, the inventor also invented "a detecting element" (disclosed in the Japanese Laid-Open Patent Publication No. SHO63-157024). This element, made of a metal (any metal, inorganic or organic), electrically detects at least one of piezoelectricity, pyroelectricity and inverse piezoelectricity phenomena occurring in the metal. In the above two pending applications, the inventor discloses the fact that piezoelectricity and/or pyroelectricity phenomena occur in electrically conducting metals and inorganic or non-organic substances with no band gap regardless of whether they are crystalline or non-crystalline, in substances composed of more than one of these metals and/or substances, and in electrically conducting metals (inorganic or organic) with a very small (narrow) band gap. The inventor also discloses the method of measuring these electrical phenomena for detecting the dynamic change macroscopically in these substances or in a structure composed of these substances, and microscopically in molecules and atoms constituting these substances.
The low impedance amplifier of the present invention is used as a low impedance amplifier including an impedance converter (with a built-in preamplifier) comprised in a circuit system, as shown in the block diagram of the structural abnormality detecting circuit in FIG. 3 attached to the Laid-Open Publication No. SHO62-259050, and in FIG. 2 attached to the Laid-Open Publication No. SHO63-157024. The amplifier of the present invention is a preamplifier necessary for electrical amplification of the electric phenomena which cannot be attained by the conventional amplifier with high impedance on the input side.
Namely, piezoelectricity and/or pyroelectricity occurring in a structure composed of the above-mentioned substances is a signal of a low impedance of the order of 1.times.10.sup.-9 to 1.times.10.sup.4 ohms. Such a low impedance signal cannot be amplified electrically by any amplifier other than a low impedance amplifier. The conventional amplifier is designed for high impedance and not for low impedance. Therefore, it cannot be used as a "low impedance amplifier" in the circuit of detecting the structural abnormality resulting from spontaneous polarization of a low impedance structure.
More specifically, the conventional method of measuring distortion of a substance or structure caused by an external force application involves, as a sensor to distortion, a piezoelectric pickup which utilizes electrical spontaneous polarization, or a strain gage which utilizes current change in a resistor. Such a sensor is attached to a substance or structure to measure the distortion by using an amplifier suitable to the sensor.
However, the piezoelectric pickup provides a high impedance. The strain gage measures distortion by sending a signal for the current change in the resistor to an amplifier through a bridge circuit.
As mentioned earlier, amplifiers for a high impedance pickup or strain gage already exist. But an amplifier for low impedance piezoelectricity or pyroelectricity does not.
As disclosed in the above-mentioned publications, electrically conducting crystalline or non-crystalline metal substances (inorganic or organic) with no band gap or with a very small (narrow) band gap generate piezoelectricity and/or pyroelectricity electrically when they are subjected to an external force. Any of the conventional amplifiers for a piezoelectric pickup or a strain gage is not suitable as an amplifier for such electrical phenomena; some provide high input impedance and the others are designed for amplification of the potential difference caused directly by current.
In other words, electromotive force by such electrical phenomena as piezoelectricity and pyroelectricity which occur in the above-mentioned low impedance substances is very small as a signal source. It is impossible to amplify this electromotive force by the conventional high impedance amplifier.